code: def helper_test_multiple_ts_duplication_equality(
      self, metric, **kwargs
  ):
      test_cases, kwargs = self.get_test_cases(**kwargs)
  
      for s1, s2 in test_cases:
          s11 = [s1.stack(s1)] * 2
          s22 = [s2.stack(s2)] * 2
          # default intra and inter
          np.testing.assert_almost_equal(
              actual=np.array([metric(s1, s2, **kwargs)] * 2),
              desired=np.array(metric(s11, s22, **kwargs)),
          )
  
          # custom intra and inter
          assert (
              round(
                  abs(
                      metric(
                          s1,
                          s2,
                          **kwargs,
                          reduction=np.mean,
                          inter_reduction=np.max,
                      )
                      - metric(
                          s11,
                          s22,
                          **kwargs,
                          reduction=np.mean,
                          inter_reduction=np.max,
                      )
                  ),
                  7,
              )
              == 0
          )
  
imports: import numpy
  import pandas
  import pytest
  from darts import TimeSeries
  from darts.metrics import metrics
label_desc: Use image node_id 6 for calling the TestMetrics obj's underlying member method code with example usage: obj.helper_test_multiple_ts_duplication_equality(metric) without return types